“Send On Behalf of” not showing up…

I am hoping someone has seen this before. Running exchange 2003. I granted a user (Coswell Cogs)send on behalf of rights via AD. The user can send on behalf of the email box in question (Cogs Support Msailbox), but the actual “Send on behalf of” does not display. It simply displays either the senders name (Coswell Cogs) or the name of the mailbox it is being sent from (Cogs Support mailbox.) The user has full mailbox rights and it is not happening to any other mailbox (that I know of.) Any help would be appreciated.